A phase change memory (PCM) is a novel nonvolatile memory that develops fastest currently. The phase change memory uses different resistance values represented by phase change materials in a crystalline state and in an amorphous state to store corresponding data, and is widely applied to a rewritable compact disc (CD) and a rewritable digital versatile disc (DVD). To meet a requirement of massive information storage, research on high-density storage of the phase change memory appears to be particularly important. Conventional methods for implementing a high-density phase change memory include reducing an area of a phase change unit and reducing an area of a peripheral circuit. The former needs to improve a component structure and is limited by a photolithography size, and the latter needs to optimize an integrated circuit design.
To resolve the foregoing problem, a multi-valued storage technology arises. Different from a conventional binary storage method, the multi-valued storage technology can make full use of a resistance difference between a crystalline state and an amorphous state of a phase change material, and store at least two bits of data in one storage unit. In the prior art, a method for implementing multi-valued storage in a phase change memory generally includes an erase process (or SET) and a write process (or RESET). The erase process is to apply a pulse with a low amplitude and a long pulse width to a storage unit of the phase change memory, so that the storage unit is in a stable low-resistance crystalline state. The write process is to apply a single pulse with a high amplitude and a short pulse width to a storage unit the storage unit is in a high-resistance amorphous state. Because a resistance value of the storage unit of the phase change memory changes according to a width and an amplitude of an applied programming pulse, by applying single-pulses with different amplitudes and different pulse widths to the storage unit, the storage unit may have amorphous states corresponding to different resistance values. The amorphous states corresponding to different resistance values correspond to different storage states, so as to implement the multi-valued storage in the phase change memory.
In the prior art, multi-valued storage is implemented using a single pulse with a high amplitude and a short pulse width. However, applying a single pulse with a high amplitude and a short pulse width to a storage unit of a phase change memory causes a temperature of the storage unit to increase extremely fast, generating thermal crosstalk.